BIN TENDER HAD MOVED CHUTE FROM TRIPPER ACROSS WALKWAY TO FILL BIN ON THE OPPOSITE SIDE AT BIN 4. DURING THIS PROCESS HE NEEDED TO STEP OVER THE TANK TO GET TO THE OTHER TRIPPER. HE SLIPPED ON GRANULE ON THE EDGE OF THE TANK TOP. AS HE WENT DOWN HE CAUGHT HIMSELF WITH HIS LEFT HAND, WEIGHT GOING ONTO THE FOURTH AND FIFTH FINGERS THAT WERE BENT UNDER.